feat: Docker-Support (Compose + Dockerfiles)
- docker-compose.yml: db (timescaledb/pg17) + backend + frontend
- backend/Dockerfile: multi-stage (golang:1.24-alpine -> debian:bookworm-slim)
- frontend/Dockerfile: multi-stage (node:22-alpine -> nginx:alpine), Build-Args fuer VITE_*
- frontend/nginx.conf: SPA-Routing + Asset-Caching
- .env.example: BACKEND_HOST, DB_PASSWORD, JWT_SECRET, API_KEY
- backend/config/config.go: ENV-Var-Support vervollstaendigt (JWT_SECRET, API_KEY, DB_PORT, DB_USER, DB_NAME)
- backend/config.yaml.example: ENV-Var Kommentare ergaenzt
- README: Docker-Quickstart als empfohlener Einstieg (3 Befehle)
- .gitignore: .env zur ignore-Liste hinzugefuegt
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